Electrical contacting devices



Jan. 24, 1956 R. s. OHL 2,732,464

ELECTRICAL CONTACTING DEVICES Filed July 18, 1951 FIG.

TO CONTROL C/RCU/ T lNVENTOR R. S. OHL

ATTORNEY United States Patent ELECTRICAL CONTACTING DEVICES Russell S.Ohl, Fair Haven, N. J., assignor to Bell Tele phone Laboratories,Incorporated, New York, N. Y., a corporation of New York ApplicationJuly 18, 1951, Serial No. 237,347

9 Claims. (Cl. 200-166) This invention relates to electrical contactingdevices and more particularly, to those in which a liquid surface isused as the contacting medium.

An object of the invention is to produce extremely fast operating makeand break contact closures in elec' trical contacting devices.

A further object of the invention is to provide an electrical switchcontact which has, and which maintains, low contact resistance, andwhich is self-healing to the effects of contact sparking.

It is well recognized that liquid contacting surfaces have distinctadvantages over solid elements as the contact making media forelectrical circuits. For instance, such liquid contacting media presenta fresh surface for each successive contact closure and are not subjectto the pitting and corroding effects that gradually reduce theusefulness of solid contact elements. With these advan tages in view,several forms of mercury switches have been devised in the past.Substantially all of these switches necessitate a pool or reservoir forcontaining the liquid mercury. The requirement of this pool necessitates specialized contacting apparatus of complicated nature for, ifthe specialized apparatus is not employed, the use of the switch isundesirably limited to operation in a single stable position.

It is, therefore, a further object of the invention to simplify andimprove electrical contacting devices emplo ing liquid contactingsurfaces.

it has been found by experiment that the metallic element gallium may beelectroplated by the special process to be described hereinafter upon abase metal contacting member. At substantially room temperatures theplated coating of gallium becomes liquid and adheres firmly and evenlyto the surface of the base metal. It has been further found that underthese conditions the gallium has a very low vapor pressure and vaporwhich may be produced from sparking at the contacting sur face israpidly condensed and added to the molten surface layers upon the basemetal member. Furthermore, it has been found that because of this lowvapor pres sure condition, the gallium does not evaporate readily toproduce an ionized conductive gas and, therefore, as a contact material,produces a very fast break and make in an electrical circuit.

The nature of the present invention, its various ob jects, features andadvantages, will appear more fully upon consideration of the embodimentillustrated in the accompanying drawings and in the following detaileddescription thereof.

Fig. 1 shows in pictorial form a simplified electrical contacting devicein accordance with the invention; and

Fig. 2 shows a self-operating contacting device in accordance with theinvention, suitable for generating high frequency pulses of electricalenergy.

Referring to Fig. 1, the contacting device comprises a cylindrical glassenvelope or capsule 12. Through one end of the capsule protrude the twoconducting elements 13' and 14 to be electrically connected. Each ofthese 2 ,732,464 Patented Jan. 24, 1956 elements is of conductingmaterial, for example nickel wire, and is sealed into the end face ofthe capsule 12 to extend a fraction of an inch therein. Located withincapsule 12 is a sphere or ball 11 of a base metal coated with gallium inthe manner to be described in detail hereinafter. The diameter of thesphere is slightly smaller than the cross-sectional diameter of capsule12, so that when the capsule 12 is turned in the position as indicatedin the drawing with electrodes 13 and 14 at the bottom, the sphere 11will rest, due to the force of gravity, upon the electrodes 13 and 14.The end of capsule 12 opposite electrodes 13 and 14 is constricted andsealed off at 18 to render capsule 12 an air-tight container for thereasons to be pointed out below.

Around capsule 12 at a position slightly above sphere ii are woundseveral turns of insulated conductor forming a solenoid 15 having endterminals 16 and 17 which are connected to the desired control circuit.Thus, when an electric current is passed through solenoid 15 by thecontrol circuit, the magnetic field developed by solenoid 15 will raisesphere 11, since the sphere is of magnetic material as will be pointedout, away from electrodes 13 and 14, breaking the electrical connectiontherebetween. When the current from the control circuit ceases, sphere11 will fall again to produce an electrical connection betweenelectrodes 13 and 14. This electrical connection is made in accordancewith the invention by the electrodes 13 and 14 contacting the liquidcoating of gallium on sphere 11. In order to provide some indication ofthe relative size of the components thus described, it should be notedthat sphere 11 may have a diameter in the order of 5 inch and the othercomponents proportioned accordingly.

Sphere 11 should be made of a magnetic base metal or alloy with whichthe element gallium will not easily amalgamate. For this purpose analloy of iron, preferably passivated and magnetic stainless steel, has,for example, been found entirely suitable.

An important feature of the invention resides in the manner in which thesmall sphere 11 of a base metal, for example, steel, is coated withgallium so that the gallium when in liquid form remains in a smooth,evenly distributed layer over the entire surface of sphere 11 Withoutforming droplets or globules which would eventually drop off or beknocked off by the physical contact of sphere 11 with electrodes 13 and14. In accordance with the invention, a suitable surface of gallium maybe deposited on a stainless steel surface by the process ofelectroplating.

The necessary electrolyte for the electroplating operation may beprepared by dissolving a small quantity of gallium metal in sulphuricacid to obtain gallium sulphate. A precipitate of gallium hydroxide isformed by adding a limited quantity of sodium hydroxide to the galliumsulphate, which precipitate is filtered and dissolved in an excess ofsodium hydroxide to form a diluted alkaline aqueous solution ofgalliumhydroxide.

After one or more steel balls, of the type to be employed for sphere 11,are thoroughly cleaned, they are placed in a rotating, non-metallicplating basket of the type commonly used by electroplaters for platingsmall objects. In general, these plating baskets are such that the smallobjects, in this case the steel spheres, are continually agitated ormoved from one position to another as the plating basket is rotated inthe above prepared electrolyte solution, while at all times makingelectrical contact at successively different points with a cathodecontact of gold alloy. The electrolyte should be at about 25 degreescentigrade. The anode comprises a small puddle of gallium metal in theelectrolyte, which puddle is contacted by an electrode of gold alloywire. A potential difference of from 1.5 to 2.0 volts is applied betweenthe anode contact or electrode and the cathode contact in the platingbasket.

When the plating is sufiicient that the steel balls show a grey matteappearance, which indicates a gallium coating thereon in the order of 1mil thickness, the steel balls are removed from the plating bath, washedand dried. At this stage, the gallium becomes slightly oxidized by theair and exhibits a light grayish color partly due to gallium oxide, arelatively high-resistance material, which must be removed before thelow-resistance gallium may be employed as an electrical contactingmaterial. This coating may be removed in several ways, such as by chernically reducing it or preferably, by some physical burnishing operationwhich removes the oxide coating. A particularly advantageous method forremoving this coating has been devised, suitable for use with theparticular embodiment of the invention shown and described here- Thus,before end 18 of cartridge or capsule 12 is in. constricted, sphere ll,including the oxidized coating of gallium thereon, is placed withincartridge 12. Cartridge 12 is evacuated by means of suitable apparatusconnected at constriction 1S and then filled with a suitable knownreducing atmosphere, for example hydrogen gas. An alternating-currentpotential, for example in the order of 60 cycles or more per second, isapplied to terminals 16 and 17 and a direct-current potential of severalvolts is applied between electrodes 13 and 14. This causes sphere 11 tovibrate incessantly in the reducing atmosphere against electrodes 13 and14. During this action sphere 11 will precess about its center due tothe vibration until electrodes 13 and 1-; have burnished or polished theentire surface of sphere l1 and distributed the gallium uniformly overthe surface. A portion of the gallium oxide will be reduced and theremainder will be flaked off and fall as a high-resistance powder to thebottom of cartridge 12. No adverse effect will be obtained if the powderis allowed to remain loose within the cartridge,

' but if desired it may be removed by withdrawing it along with thehydrogen atmosphere. If this is done, the cartridge should be refilledwith an inert gas such as nitrogen to prevent further formation of oxideon the surface of sphere 11. If allowed to remain within the cartridge,the reducing atmosphere will also serve this function.

It should be noted that the present invention contemplates operationunder ambient temperature conditions at which the gallium coatingabove-described will be liquid. it has been determined that the meltingpoint of gallium is approximately 29.8 degrees centigrade. Under normalconditions, particularly considering the heat which will be generatedover a period of'operation by electrical sparks in the contact area,this condition of ambient temperature will be readily met. However,under unusual conditions of operation, external heat may be supplied inany Well-known manner.

The invention has thus been described with reference to a particulartype of contacting device which appears of particular advantage inutilizing the unusual properties of the contacting material gallium inaccordance with the invention. it should be readily apparent, however,that many other contact shapes and forms other than the spherical shapeherein disclosed may likewise be plated with gallium in the mannerdescribed to obtain the desirable results described herein. Furthermore,for the sake of simplicity of description, a type of electricalcontacting device in which the restoring contact force has been suppliedby gravity has been chosen to illustrate the invention. It should beapparent to one skilled in the art how the invention may be adapted tospring contacting devices or to those contacting devices in which theoperating force for either making or breaking of the contact, or both,is supplied by an electromagnetic field.

Fig. 2 shows a particular contacting device in which the, operatingforce is electrostatic and which device may become self-operating insuch a way as to generate a series of high frequency pulses ofelectrical energy. A capsule comprising a glass cylinder 22 sealed ateach of its ends by metal end members 25 and 26, is similar to thecapsule 12 of Fig. 1. Extending one at each end Within the capsule222526 are conducting electrodes 20 and 21. As shown in Fig. 2,electrodes 26 and 21 protrude at the bottom and top ends, respectively,of capsule 22 and may be spot welded, for example, to the inside centersof end members 26 and 25. Connections for supplying an electricalpotential to the electrodes 20 and 21 may also be connected to the endmembers 26 and 25. Located within capsule 22 of Fig. 2, are two spheres18 and 19, each shaped, proportioned, and coated with the metal gallium,in the manner hereinbefore set forth for sphere 11 of Fig. l. Thesurface of gallium on spheres 18 and 19 of Fig. 2 is prepared in themanner set out above and the capsule 22 is evacuated or preferablyfilled with an inert gas such as nitrogen to about 10 atmospheres inaccordance with the considerations already defined, before the endmembers 25 and 26 are sealed to the cylinder 22.

The spheres 13 and 33 are shown in Fig. 2 in an at rest position inwhich the spheres are in contact with each other and with electrode 20due to the force of gravity. However, when a high direct-currentpotential is applied bl tween electrodes 26 and 21, with a polarity, asshown in Fig. 2, of minus and plus, respectively, sphere 1) will becomenegatively charged and will then be immediately attracted byelectrostatic force to the positively charged electrode 21. Upon contactwith electrode 21, sphere 19 will become positively charged. Thereupon,an electrostatic attraction will be set up between the positivelycharged sphere 19 and the negatively charged sphere 18. The spheres willleave their respective electrodes, meeting at a point mid-way betweenthe electrodes and will discharge to produce a damped radiation at awavelength which is 211 times the diameter of the spheres. After theyare discharged, they are again attracted to their respective electrodeswhere they recharge with'a subsequent repetition of the dischargeprocess.

It may be shown that the pulse power in watts obtainable from the seriesof discharges between the spheres is equal to 2.2l \NE 10* where E isthe potential difference in volts between the two electrodes 2:) and21.. where N is the number of discharges per second, and where is thewavelength of the radiation when two spheres mutually discharge eachother. A substantial portion of this power may be launched in awaveguide ransmission system, such as wave-guide section of Fig. 2, bylocating capsule 22 within the wave guide 23 and extending ittransversely thereacross. A piston, such as 24, tunes the impedance ofguide 23 to that of the generator.

In all events, it is to be understood that the abovedescribedarrangements are illustrative specific embodiments of the principles ofthe invention. Numerous other arrangements may be devised by thoseskilled in the art without departing from the spirit and scope of theinvention.

What is claimed is:

1. An electrical contacting device comprising a pair of metallicelements, a base metal member arranged to make contact with both of saidelements, anelectroplated layer of the element gallium upon said basemetal member to make-electrical connection between said elements, andmeans for moving said base metal member away from said elements to breaksaid electrical connection. 7

2. An electrical contacting device comprising a pair of metallicelectrodes, a sphere of base metal resting upon at least one of saidelectrodes, an electroplated layer of the element gallium upon saidsphere, and means for raising said sphere off said electrode.

3. An electrical contacting device comprising a pair of metallicelectrodes, a sphere of base metal resting upon one of said electrodes,a second sphere of base metal resting upon said first-named sphere, acoating of the element gallium upon each of said spheres, adirect-current potential connected between said pair of electrodes, andmeans for raising said spheres ofi said electrode comprising theelectrostatic field set up between said spheres and the other of saidpair of electrodes.

4. In combination, an electrical contacting device having metalliccontacting elements, an electroplated layer of the element gallium uponat least one of said elements, means for enclosing said contactingelements in an atmos" phere of an inert gas, and means for operatingsaid contacting device with the elements so enclosed.

5. An electrical contacting device comprising a pair of metallicelectrodes, a base metal member contacting at least one of saidelectrodes, an electroplated layer of the element gallium on said basemetal member, and means for moving said bas'e'metal member out ofcontact with said electrode.

6. An electrical contacting device comprising a pair of metallicelectrodes, a first base metal member contacting one of said electrodes,21 second metal base member contacting said first base metal member, acoating of the element gallium upon at least one of said base metalmembers and means for moving said first base metal member out of contactwith one of said electrodes.

7. In combination a pair of base metal electrical contacting members,and an electroplated layer of the element gallium upon at least one ofsaid members.

8. An electrical contacting device as in claim 5 wherein the base metalmember is in the form of a sphere.

9. An electrical contacting device comprising, in combination, a pair ofmetallic electrodes, a first movable base metal member contacting one ofsaid electrodes, a second movable base metal member contacting saidfirst base metal member, a coating of the element gallium upon at leastone of the said movable base metal members, and a means for moving saidsecond base metal member out of contact with said first base metalmember and into contact with said second electrode.

References Cited in the file of this patent UNITED STATES PATENTS627,475 Brown June 27, 1899 1,948,687 Swinne Feb. 27, 1934 2,175,354Lewin Oct. 10, 1939 2,309,953 Harrison Feb. 2, 1943 2,327,870 Coxe -4.Aug. 24, 1943 2,488,928 Packard Nov. 22, 1949 2,501,164 Durst Mar. 21,1950 2,545,352 Gibbs Mar. 13, 1951

